Create README.md

README.md

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+# Partial Expressions - Babel plugin
+
+Try it in this **[babel playground](https://babeljs.io/repl#?browsers=defaults%2C%20not%20ie%2011%2C%20not%20ie_mob%2011&build=&builtIns=usage&corejs=3.6&spec=false&loose=false&code_lz=CwJgUABBA-B8EH0IGoIHICEbI3gYwHsA7AZwIBsBTAOnIIHMBuIA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=true&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=env%2Cstage-0%2Cstage-1&prettier=false&targets=&version=7.13.17&externalPlugins=%40kosich%2Fbabel-plugin-partial-expressions-experiment%400.0.1)**.
+
+Or install it via
+
+```
+npm i @kosich/babel-plugin-partial-expressions-experiment -D
+```
+
+And then add it to your `babel.config.json` as [described here](https://babeljs.io/docs/en/plugins).
+
+_NOTE: put it before pipeline operator plugins, if you use those._
+
+## About
+
+Partial expressions is a syntax sugar to simplify writing expression that are awating one additional variable, e.g.:
+
+```js
+let bang = _ + '!';
+// equals to
+let bang = x => x + '!';
+```
+
+As a partially applied function:
+
+```js
+let bangLog = console.log(_, '!');
+// equals to
+let bangLog = x => console.log(x, '!');
+```
+
+And as a context of application:
+
+```js
+let toBase16 = _.toString(16);
+// equals to
+let toBase16 = x => x.toString(16);
+```
+
+It is also compatible with the [pipeline operator](https://github.com/tc39/proposal-pipeline-operator):
+
+I tried to cover two special cases for pipes.
+
+When the partial expression is in the **subject** of piping:
+
+```js
+let fn = _ |> increment |> console.log;
+// equals to
+let fn = x => (x |> increment |> console.log);
+```
+
+And when it's in a **pipe**:
+
+```js
+let value = 42 |> _ + 1 |> console.log;
+// equals to
+let value = 42 |> (x => x + 1) |> console.log;
+```
+
+.
+
+Similarly, we could do partial application:
+
+```js
+42 |> console.log(_, '!');
+// equals to
+42 |> (x => console.log(x, '!'));
+```
+
+And as a context:
+
+```js
+42 |> _.toString(16) |> _.toUpperCase();
+// equals to
+42 |> (x => x.toString(16)) |> (x => x.toUpperCase());
+```
+
+## Rules
+
+1. Expression is considered partial if an unbound `_` symbol is used in it.
+
+2. Expression boudaries are limited by following:
+
+    2.1 root of an expression    
+    `let a = _ + '!'` equals `let a = x => x + '!'`
+
+    2.2 body of a function    
+    `let b = x => _ + '!'` equals `let b = x => n => n + '!'`
+
+    2.3 pipe in pipeline operator    
+    `42 |> _ + 1 |> console.log` equals `42 |> (x => x + 1) |> console.log`
+
+## The End 🙂